Restoring mechanisms, also known as “overcenter mechanisms,” “snap springs,” “snap blades,” and the like, are components of many devices, including valves and electrical switches.
Monostable mechanisms are known. For example, a rigid support can be overlaid by a membrane with projections that restore push buttons, such as those of a telephone keypad, back to an undepressed position. However, such designs lack a second stable position as in a bistable mechanism.
Discontinuous cantilever bistable mechanisms are known, wherein discontinuous cantilevered tongues are held in relation to each other by a surround fashioned from the same sheet as the cantilevers. These discontinuous cantilevers can impart bistable movement to a notched rod captured between the tips of the cantilevers. Discontinuous cantilevers can be undesirable, however, for applications needing a smooth surface on the bistable mechanism.
Dome-like bistable mechanisms, including linear and planar arrays thereof, have been fabricated of thin sheet metal. However, common materials typically limit the height of the dome to about 10% of its diameter, and consequently the maximum throw can be limited to about twice the dome height (hence, about 20% of a diameter).
Disk-like bistable mechanisms are known where a disk is buckled by insertion into a circular housing slightly smaller than the disk. Alternately, or in conjunction, disk mechanisms can be buckled by introduction of a part, such as a rod, that radially displaces portions of the mechanism. These designs can require assembly and one or more additional parts for proper function, and can have limitations similar to dome-like mechanisms.
A micromechanical continuous buckled beam mechanism includes a bistable bridge spanning a recess in an underlying support material. Such a design includes at least two parts (the bridge and the rigid support which must be assembled). Moreover, the rigid support can be unsuitable for applications requiring flexibility and/or for macroscopic applications where the added weight of the rigid support is undesirable.
Piezoelectric actuators are known, but can be expensive and bulky, and can require complicated control electronics. Shape memory alloy actuators are known, but can involve significant amounts of heat generation and can have high power requirements, and can be limited in frequency. For example, maintaining a stable position with existing shape memory actuators can require continuous input of power, which can be undesirable for portable applications and can generate undesirable amounts of heat. Moreover, the operation frequency of shape memory actuators can be limited by heat dissipation because the alloy needs to cool below its activation temperature before the actuator can be operated again.